This invention relates to fiber-reinforced thermoplastic composites. In another aspect it relates to a process for forming fiber-reinforced thermoplastic composites.
Processes are known in which fiber-reinforced composites are formed by compression of the fiber reinforcement between sheets of thermoplastic resin. Multi-layer stacks of resin sheets and fiber reinforcement sheets allow the thickness of the composite to be varied. Suitable thermoplastic resins are exemplified by those such as polyolefins, polyesters, polyamides, polysulfones, poly(arylene sulfides), and polyacrylates.
The greatest usefulness of composites is in weight-sensitive high-performance applications subject to the limitation of the resin melting temperature. For example, maximum constant operating temperatures of available composites generally are in the range of from 265.degree. to 300.degree. F. Composites with higher use temperatures are desirable.
A poly(arylene sulfide ketone) resin with a melting point over 350.degree. C. (622.degree. F.) is mentioned in U.S. Pat. No. 3,819,582 as being moldable at 370.degree. C. (698.degree. F.) into a brittle film. Such brittle films cannot usually be melt processed further to form useful products. U.S. Pat. No. 4,590,104 discusses melt impregnation of fiber rovings with a low-molecular weight poly(arylene sulfide ketone) resin to form a fiber composite that exhibits after curing high toughness and good dimensional stability under heat and good solvent resistance. The curing is a requirement undesirable in the formation of composites since it adds time and therefore expense of making parts. In addition the increase in the glass transition temperature said to occur during curing indicates an alteration of the polymer.